<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

<input type="text" placeholder="半径" id="a">
<input type="text" placeholder="周长" id="b">
<input type="text" placeholder="面积" id="c">

</body>

<script>
var p =prompt("请输入圆的半径");
    var d =Math.PI;

////半径
//console.log(p);
////周长
//console.log(2*pi*p);
////面积
//console.log(p*p*pi);

    document.querySelector("#a").value = p;
    document.querySelector("#b").value = p*2*d;
    document.querySelector("#c").value = d*p*p;

</script>
</html>